How black holes went from creating stars to extinction

Astronomers have long sought to understand the beginnings of the universe, and thanks to the James Webb Space Telescope (JWST), a critical piece of the puzzle has come to light. The telescope’s infrared detection “eyes” spotted a set of small red dots, identified as being among the first galaxies to form in the universe.

This surprising discovery is not just a visual marvel, it’s a clue that could reveal the secrets of how galaxies and their enigmatic black holes began their cosmic journey.

“James Webb’s astonishing discovery is that not only does the universe have these very compact, bright infrared objects, but these are probably regions where huge black holes already exist,” says Mitch Begelman, member of JILA and professor of astrophysics at the University of Colorado at Boulder. “We thought it was impossible.”

Begelman and a team of other astronomers, including Joe Silk, professor of astronomy at Johns Hopkins University, published their findings in Letters from the astrophysical journal, suggesting that new theories of galactic creation are needed to explain the existence of these enormous black holes.

“Something new is needed to reconcile the theory of galaxy formation with the new data,” says Silk, the lead author of the potentially groundbreaking study.

The traditional tale of galaxy formation

Astronomers had already postulated somewhat orderly evolution when thinking about galaxy formation. Conventional theories believed that galaxies formed gradually, assembling over billions of years. In this slow cosmic evolution, the stars were thought to emerge first, illuminating the primordial darkness.

“The idea was to go from this first generation of stars to galaxies becoming truly dominated by stars,” adds Begelman. “Then, toward the end of that process, you start building these black holes.”

Supermassive black holes, these enigmatic and powerful entities, were thought to appear after the first stars, growing quietly in the galactic core. They were considered regulators, sometimes taking action to temper the formation of new stars, thus maintaining a galactic balance.

Challenge preconceived ideas

Through observations of JWST’s “little red dots,” researchers discovered that the universe’s earliest galaxies were brighter than expected, as many showed stars coexisting with central black holes called quasars.

“Quasars are the brightest objects in the universe,” Silk explains. “They are the products of gas accretion onto massive black holes in the cores of galaxies that generate immense luminosities, dwarfing their host galaxies. They are like monsters in a cuckoo’s nest.”

Noting the coexistence of stars and black holes, researchers quickly realized that conventional theories of galaxy formation must be wrong. “(This new data) seems (the process) to be reversed, that these black holes formed with the first stars, and then the rest of the galaxy followed,” says Begelman. “We say that the growth of the black hole, at first, favors the formation of stars. And only later, when conditions change, does it turn into a mode of star extinction. “

From this proposed new process, the researchers found that the relationship between star formation and black hole formation appeared closer than expected, as each initially amplified the growth of the other via a process known as positive feedback.

“Star formation accelerates massive black hole formation, and vice versa, in an inextricably linked game of violence, birth and death that is the new beacon of galaxy formation,” says Silk.

Then, after almost a billion years, the feeder giants became suppressive, depleting their galaxies’ gas reservoirs and extinguishing star formation. This “negative feedback” was due to energy-saving outflows – powerful winds that blew gas out of galaxies, depriving them of the material needed to create new stars.

A new galactic timeline

Building on the revelation of the nurturing behavior of black holes, the researchers proposed a new timeline for the transition from positive to negative feedback at the start of galaxy formation. By examining the different light spectra and chemical signatures emitted by these “little red dots,” the researchers suggested that this change occurred about 13 billion years ago, a billion years after the Big Bang, a period that astronomers classify as “z ≈6”. “

Identifying this transitional epoch helps astronomers target specific periods in the history of the universe for observation. It can guide future observational strategies using telescopes like JWST and others to more effectively study the early universe. Additionally, by understanding when this change occurred, astronomers can better contextualize the characteristics of modern galaxies, including their size, shape, star composition, and level of activity.

Validate a new process

To validate this new theory of collaborative galactic formation between stars and black holes, and better understand the processes involved, computer simulations are necessary.

“It will take time,” Begelman says. “Current computer simulations are rather primitive and you need high resolution to understand everything. This requires a lot of computing power and is expensive.”

Until then, the astronomical community can take further steps to examine and validate this new theory.

“The next steps will come from improving the observations,” adds Silk. “The full power of JWST to study the spectra of the most distant galaxies will be harnessed over the coming years.”

Both Begelman and Silk are optimistic that the proposed idea will be adopted by the rest of their field.

“As far as I know, we are the first to go in such an extreme direction,” adds Begelman. “I’ve kind of pushed the boundaries over the years with my collaborators working on this problem of black hole formation. But JWST shows us that we haven’t thought outside the box enough.”